Purification of the two classes of oligonucleotidyl-iodopeptidyl complexes which are present in mammalian thyroids will be continued using conventional nucleic acid methods of extraction and chromatography. For comparison, methods used in protein isolation will also be employed to purify the larger of the complexes. In vitro aminoacylation and protein biosynthesizing systems will be used to continue study of the biological effects of complex II and to search for biological role for complex Ia. Purification of several aminoacyl-tRNA synthetases from thyroid will continue. Two unstable synthetases, aspartyl- and isoleucyl-, will be used to study the mechanism of action of complex II as a possible controlling factor of this, the first step of protein biosynthesis. Tyrosyl-tRNA synthetase, already highly purified, will be used to examine in detail the mechanism of apparent aminoacylation of complex II with tyrosine. BIBLIOGRAPHIC REFERENCES: Comparison of Porcine Liver tRNA Preparations: Purification of tRNA and its Separation from RNA-peptidyl Complexes, Eileen P. Kelly and Fredrick J. Kull (1976), Analytical Biochemistry.